26 replies to this topic

[fruitfulsteve]

Has anyone tried covering shells with cotton(old shirts or sheets etc)
My plan is to make the case as normal(2xcard half's glued together) then soak the cotton with PVA or paste(probably PVA) then wrap it down over the shell from the top smoothing as i go and trim it round the time fuse this could be repeated several times until sufficient size and strength is obtained obviously this is not possible with paper due to the fact that it would rip.

Comments please

Obviously other materials could be used,but cotton is more eco friendly

[phildunford]

Never tried it, but sounds like it could be quick and strong.

Would love to hear how you get on.

[T-sec]

This way of working 'could' be an option to paste your shells a bit fater, more nice and maybe even stronger.

But beware of the break characteristics using 'alien' pasting materials.
The breaks can be less good, or even partial distroy your stars due to higher pressure build up, etc.

Next to this, the solvents in the cotton pasting fluid can reach the shell's inside through the paper casing, and affect the stars.
The result can be that due to the solvent gasses the stars burn in less good colors, or even will not burn/ignite at all.
When using this kind of shell pasting, leave your shells to dry for at least a week in an dry and warm earea to be sure.

I should say: give it a trial by error, and report us afterwards.

[pyrotechnist]

Can you not get hold of plaster bandages? wouldn't that be of a similar idea accept you just wet it and apply. They should dry rock hard.

[fruitfulsteve]

Good point
I'll try a few with gum arabic bound stars,and maybe just 2 layers of cotton. I'm pretty sure that PVA should be ok i've used it before to glue shell cases.
H3 burst, AP prime, i was going to use chlorate stars but i may opt for perchlorate as i'm using gum arabic as the binder.

Now to raid the lining cupboard

[fruitfulsteve]

Can you not get hold of plaster bandages? wouldn't that be of a similar idea accept you just wet it and apply. They should dry rock hard.

Not really as they come in strips and the idea is to cover the whole shell in one go.

I do have a load of arm sling bandages i may try some of those.

[Mortartube]

If you get viscose rayon it should harden when you apply acetone. It was propsed as a replacement for plaster casts a few years ago.

[fruitfulsteve]

If you get viscose rayon it should harden when you apply acetone. It was propsed as a replacement for plaster casts a few years ago.

Does it come in sheets or strips,also i don't think it sounds very bio degradable,i don't want another telling off from the enviro pyros

[Arthur Brown]

I saw an insert/bombette from a cake and it was a paper bag as you describe with many layers like an onion. Opposite the fuse there was a smooth surface, but where the layers came towards the fuse there was a lot of paper to lose.

Don't use any thing that makes shrapnel, Paper is used because it does the job with least residual debris. and the debris is soft!

[fruitfulsteve]

This is why i think cotton sheet not paper is the way to go as you'd need fewer layers and therefore less build up at one end you can also alternate the sheets when/if more than 2or3 layers are needed by making a small hole in the centre of the sheet that go's over the time fuse. I don't think vaporised cotton sheet even when coated with PVA could be classed a shrapnel and definitely woulndn't be heavy enough to cause any serious damage.

If this works i bet their will be a few W.A.S.P owners out their kicking themselfs

Perhaps a layer of nitrated cotton sheet on the outside might make for a good effect too.

[a_bab]

"Perhaps a layer of nitrated cotton sheet on the outside might make for a good effect too."

Yeah, why shoudn't we soak the whole thing in nitroglycerine I guess we are derailing here.


Well, I did it. I mean I pasted shells with cotton strips.

I used several layers of about 1.5" cotton "tape" I had specifically got for this.
I don't have too much time for (this) hobby, so I try to make the things as fast as possible. Usually I'm left with a few days by the end of the year, after begging my wife in the knees and selling my soul/promissing things I'll do for the year to come, only to regret it later amazed how coud I I had promissed so many. In these few days (usually 3-4) I'm supposed to build my stuff from scratch (stars, hemis, BP, hulls, everything).

I hate the idea of plastic shells, as any kind of pollution for that reason. Plastic shells is the way to go for the less fussy if speed is needed. Nothing can beat it.
But for the enviromentalist I am cotton sounded as something that would be better assimilated by the nature in my lifetime.

The basic idea was to paste the shell pretty much like a WASP machine would do with the dry cotton tape and then paint with sodium silicate between the layers. While it was possible to paste 6 pieces of 4" shells with 6 layers each in 2 hours, it didn't work quite as expected. 24 hours wasn't nearly enough to fully dry the layers. Nevertheless the shells worked as expected, with good breaks (fairly simetrical too). I chose sodium silicate as I had the (false) impression that it'll dry quickly.

The next day I collected the debris for a further analysis (who doesn't?) and it was then I discovered the sodium silicate is in no way good to replace the old paste, as it makes everything very brittle (paper even more so), thus affecting the performance.

Using PVA or some other kind of fast drying glue would work for sure, especially if dried beween layers.

Unfortunately this forum doesn't seem to allow pics attaching and I'm way too lazy to upload them somewhere else.

[fruitfulsteve]

Damn you got their before me.
Allthough my plan did not involve the use of strips, but a sheet large enough to wrap one layer each go,anyway your test seems to indicate that it is plausable and should work but i do think PVA would be better(and dry harder and be more water resistant)
Also iv'e had another thought, that is to use old (preferably cotton) socks also coated in PVA and the pull tight over the shell casing fastened with tie wire or cable ties and trimed around the time fuse (streching i think will be important to take up any elastication in the material) obviously this may restrict the size of shell (dependant on foot size) but i'm sure their are other of the shelf cotton items that would also work for larger shells(failing that just hang around the changing rooms of the new zealand rugby team)

[a_bab]

The problem with using large sheets of cotton cloth is that the wrinkles would be very difficult to smear, as it doesn't work like paper. They will pop back no matter how much glue you use, and they'd also take lots of volume, making the shell "fluffy".

There's another technique I saw described somewhere if you hate pasting, involving PVA glue and wood meal. It works for making hemis too. I'll go into detail if you are interested. It's not mine, but I'm fairly sure I saw it on this forum.

[Mortartube]

Does it come in sheets or strips,also i don't think it sounds very bio degradable,i don't want another telling off from the enviro pyros

It's a synthetic material that clothing is made from. Primarily skirts, dresses and trousers.

Edited by Mortartube, 20 November 2009 - 08:55 PM.

[fruitfulsteve]

I see what you're saying,but using the technique (explained earlier in the thread) i think that problem can be overcome.
What do you think of the sock idea?